Transcript Cell Division

Cell Division
LG4: Understand cells’ role in
living things and heredity.
A Question…..
What do you,
an ant,
and an oak tree
have in common
(talk to a partner)?
An Answer….
Yes, you are all living things…but more
importantly
You are all made of trillions of cells!
AND
you all started out as a single cell!
Cell Theory
In the 1830’s
Theodor Schwann
& Matthias
Schleiden
proposed “Cell
Theory”
Cell Theory states…
1.
2.
3.
All living things are made of
cells.
Cells are the basic unit and
function of all living things.
Living cells only come from other
living cells.
Cell
Zygote
Division…
How do you become a
multicellular organism if
you started out as just
ONE cell (talk to a
partner)?
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Through cell
division, a
single cell
becomes two
cells. Those
two cells divide
into four….
Time for math…
how many cells
would you have
after 6
divisions?
How Many?
You would
have 64
cells!
Cell Division
Cells multiply by dividing!
Answer (talk to your neighbor):
• How does your drawing show that
cell division can cause organisms to
grow larger in size?
• Is there a limit to how large a cell
can be? Why or why not?
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Consider….
What are the purposes
of cell division?
Regrowth/growth
 Repair
 Reproduction
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(Hint: This is important!)
Regrowth/Growth
How tall were you when you were 5?
How tall were you last year?
How tall are you now?
Do you think: Your cells got bigger?
or
Your cells divided to produce more cells?
(talk with a neighbor)
Regrowth

While individuals grow in size, a
larger organism has MORE
CELLS than a smaller organism
There are limits on how big a
cell can get. What do you think
is the main reason why cells
only get to be a certain size?
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Regrowth
Cells continue to divide to help an organism or
part of an organism grow
As the cell grows, more processes are needed
for it to function, so its demand for instructions
increases. However, the amount DNA
(instructions) remains constant. The
instructions will determine what type of cell it
becomes.
Specialization
We know that cells divide in order to make
bigger organisms. However, if cell division
were the only process occurring in cells,
all multicellular organisms would end up
as spheres of identical cells.
During development, cells become
specialized to perform particular functions.
In Other Words….
Cells get instructions from DNA about
what type of cell it will become and
what will be its function!
Cell Types
Some cells might
become layered
skin cells, while
others might
become long, thin
nerve cells.
Red Blood Cells
Cheek Cells
Nerve Cells
Bone Cells
One purpose of cell division
Regrowth
Next reason…
Repair
Have you gotten a
paper cut recently?
Have you broken a
bone in your arm
or leg?
Repair

The body repairs injuries like
these by means of cell
division. For example…….
When your skin is cut, skin cells
on either side of the cut make
new cells to heal the wound.
Repair
As cells age and die, they need
to be replaced.
In the human body:
-There are about 200 different
types of cells (remember the
pictures?).
-Every minute or so, your skin
loses about 40,000 cells!
-In contrast, your brain cells live a
very long time!
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One purpose of cell division
Regrowth
Next reason…
Reproduction
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In order for organisms to reproduce,
reproduction (sex cells – meiosis) must occur
Reproductive cell division produces sex cells
with ½ the genetic information from each parent
(humans – 23 from mom / 23 from dad)
Summary…
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Cells are the main
components of all living
things
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The purpose for cell
division:
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Regrowth
Repair
Reproduction
Cell Cycle
Mitosis in Words
Interphase
Cytokinesis
Cell grows, makes a copy of DNA.
(90% of cell’s life is spent here!)
Cell membrane pinches in two; each
daughter cell has same number of
identical chromosomes.
Prophase
The Cell Cycle
Chromosomes and spindle
fibers form; nuclear envelope
breaks down.
Metaphase
Telophase
Chromosomes stretch out;
new nuclear envelope forms
around chromosomes.
Anaphase
Centromeres split;
chromatids separate and
move to opposite ends.
Chromosomes line up
across the center and
attach to a spindle fiber.
Length of the Cell Cycle
Mitosis
One More Look at Mitosis
Meiosis (“my-o-my! Sex Cells!)
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The process by which the number of
chromosomes is reduced by half to form sex
cells (sperm and egg)
Chromosome pairs separate and are
distributed to two different cells.
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The resulting sex cells have only half as many
chromosomes as the other cells in the organism.
Meiosis

Requires two
divisions of the
nucleus
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Meiosis I- (Just
like mitosis)
Meiosis II- two
daughter cells go
through a second
division of the
nucleus. (during
this process,
there is no
chromosome
replication)
Meiosis II (after Meiosis I
which is Mitosis)
The difference between
Mitosis and Meiosis
(W.U. - copy this slide into notes)
Mi”T”osis
(“T” is for TWIN!)
Meiosis
(“MY-OH-MY! SEX CELLS!)
•One
•Two
division of the
nucleus = 2 cells
for growth and repair
•Creates exact “T”win of
cell (diploid cells)
divisions of the nucleus
(mitosis, THEN meosis = 4 sex cells
cells)
•Used
•Used
for sexual reproduction
•Creates
cells with ½ genetic material
(haploid cells) – in humans, 23
chromosomes from each parent = new
human with 46
•Cancer is Uncontrolled
Mitosis:
Mitosis must be controlled,
otherwise growth will occur
without limit (cancer)
•Mutations in control
proteins can cause cancer
Cancer Cells – What is it?
Cancer is a disease in which cells grow and divide
uncontrollably, damaging the parts of the body around
them. It is caused by a mutation that causes uncontrolled
mitosis.
Mutations
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A mutation (from Latin word that means change) is any
change in a gene or chromosome.
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Can cause a cell to produce an incorrect protein
during protein synthesis.
As a result, the organism’s trait, or phenotype,
may be different from what it normally would have
been.
Results of Mutations
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If a mutation occurs in a SEX CELL, the
mutation can be passed on to an offspring
and affect the offspring’s phenotype.
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If a mutation occurs in a BODY CELL, the
mutation will not be passed on to the
organism’s offspring.
Effects of mutations
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Introduce change in an organism (genetic
variation)
Can be harmful (reduces the organism’s chance for
survival and reproduction)
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Can be helpful (improve an organism’s chance of survival and
reproduction)
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Antibiotic resistance in bacteria
Can be neither harmful nor helpful
Rate Yourself!
LG4: Understand cells’ role in living things
and heredity.
“Before this presentation, I was a _____
because I knew __________ about cells.
now, I feel like I am a _____
because I
learned
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